The main significance of the Spanish Inquisition is that it shows the deadliness of religion as a tool for power. As a succession of Popes tried to suppress the Inquisition, it only gained power with its two weapons of fear, surprise, and ruthless efficiency. However, the reports of torture in the Spanish Inquisition are suggested by modern scholars to be grossly exaggerated. Torture (the three main methods of which were garruto, or the suspension of the victim from the ceiling by the wrists, toca, or waterboarding, and potro, or the rack) was used in only two percent of cases, lasting no longer than fifteen minutes. In less than one percent of cases was torture used a second time, and never more than twice. Despite this, the death toll of the Inquisition was very high and set the example for many future witch-hunts. These included the famous paranoia that would occur in Salem, Massechusets. The paranoia that swept Spain during the rule of the Inquisition was similar to this, as was the tendency of people to report their neighbors for personal reasons rather than actual suspected witchcraft or heresy. Ultimately, the Inquisition is proof that religion is the most powerful and deadly when wielded for political reasons, as monarchs had more resources and tangible power than the Pope. It would have been easy for King Ferdinand to prevent the Pope from starting an Inquisition in Spain, but when Ferdinand set up an Inquisition, the Pope was powerless.
http://www.youtube.com/watch?v=89Xv4mV1BIs: an educational song about the Spanish Inquisition